Addition agent for acid copper electrolytes



Current Density s pi. is, 1958 R. E. HARROVER, JR 2,853,443

ADDITION AGENT FOR ACID COPPER ELECTROLYTES Filed April 25, 1956 Fig.l.

Acid Copper Electrolyte Plus on Addition Agent Fig.2.

Cathodic Cathodic X-Ploting Time Between iOO Seconds und Second Y Between I00 Seconds ond Sec. Y

I Anodic Anodic X-Ptoting Time A Y'Deploting Time at ledst of X WITNESSES INVENTOR Robert E. Hdrro'ver, Jr.

United States PatentO ADDITION AGENT FOR ACIDCOPPER ELECTROLYTES Robert E. Hal-rover, Jr., Wilkinsburg, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 25, 1956, Serial No. 580,612

16 Claims. (Cl. 294-52) The present invention relates to depositing copper from acid electrolytes, and has particular reference to novel products adapted for addition to acid electrolyte plating baths whereby brighter and smoother copper electrodeposits are obtained.

Heretofore, numerous addition compounds have been suggested for incorporation in acid copper electrolytes for the purpose of providing improved deposition of copper on articles therefrom. The addition compounds suggested heretofore have not been completely satisfactory.

For example, only a meager improvement in brightness and smoothness has been obtainable with certain of the addition agents suggested in the prior art. Moreover, the bright range obtainable with some of these agents is relatively narrow and in some cases the throwing power of the bath has actually been reduced.

, Another disadvantage attendant with the use of many of. the addition agents now commercially available is that the copper deposited from electrolyte baths containing such agents frequently tends to be quite brittle. T his brittleness is undesirable in that it makes machining or other processing of members plated with such copper quite diificult. Striations and ribs also commonly result when plating from acid copper electrolytes containing many of the previously known addition agents. 7

The object of the present invention is to provide com pounds comprising the reaction product of an alkylolamineand a compound having the nucleus iii which compounds are suitable for addition to acid electrolyte plating baths to promote brighter andsmoother electrodeposition.

Another object of this inventionis to provide a process for preparing a reaction product of an alkylolamine and a compound having the nucleus agent comprising the reaction product of analkylolamine and a compound having the nucleus gig:

said addition agent being present in. annamount sufli cient to promote brighter and smoother icopper electrodeposition.

Fig. 2 is a graph ilustrating one type of periodic reverse current electroplating.

In the attainment of the foregoing objects and in accordance with. the present invention, there are provided novel reaction products suitable for addition to acid electrolyte plating baths in specified amounts to promote brighter and smoother copper electrodeposition.

The novel reaction products are obtained by reacting substantially equimolar quantities of .at leastone com pound having the nucleus iii-ti The inclusion of these reaction products in the elec trolyte provides a bath with relatively high throwing power. Furthermore, the bright range at both the high and low current density ends is extended beyond the limits normally attained with presently available addition agents. The relatively high throwing power and the extension of the bright range make it possible to plate all the surfaces of members having recesses, which are low current density areas, with uniformly bright and smooth deposits. The high current density extensions of the bright range also permits higher than normal current densities to be used, thus affording a savings in deposition time for any given thickness of plate.

Another advantage resulting from the incorporation of these addition agents in acid copper electrolyte is the improvement in the but'iability of the copper deposited; Usually the copper deposited from plating baths containing the addition agents of this invention is so bright that it requires no bufiing at all. However, should a full bright plate not be obtained for one reason or another, the copper deposit isof such high quality and fine grain that only a very light buffing operation is necessary to prepare it for subsequent bright deposits of nickel, chromium or the like;

In preparing the novel reaction products of this-invert tion, any of the several compounds having the nucleus "iiimay be reacted with an alkylolamine as will be described more fully hereinbelow. An example of a particularlysuitable aliphatic compound having the nucleus i t is acetylthiourea.

Examples of other co-mpoundshaving the nucleus" ONC III HS are l-thiohydantoin and substitution derivatives of 2-thiohydantoin having at least one organic substituent Patented Sept. 23, 1958 in the 1,5 positions. The nucleus of these Z-thiohydantoin substitution derivatives has the following structure:

Various organic radicals may be substituted at one or both of the 1 Or positions, so long as the compound is not rendered so insoluble that it Will not dissolve in the acid copper electrolyte in an amount sufficient to produce an appreciable improvement in brightness and smoothness of the copper deposited. Examples of suitable compounds are:

Z-thiohydantoin l-acetyl-Z-thiohydantoin 5 2-hydroxylbenzal) -2-thiohydantoin 5-furfural-Z-thiohydantoin S-benzal-Z-thiohydantoin l-methyl-2-thiohydantoin Other examples of compounds having the nucleus -ON-G- ii is i which are suitable for reaction with alkylolamines to produce novel compounds of this invention include 2-thiobarbituric acid and substitution derivatives of Z-thiobarbituric acid. The nucleus of these Z-thiobarbituric acid derivatives has the following structure:

Various organic radicals may be substituted for hydrogen at any one or more of the 1, 5, or 6 positions, providing the resultant compound obtained upon reaction with the alklolamine is soluble in the acid electroplating bath. Examples of suitable compounds of this nature include:

Z-thiobarbituric acid l-acetyl-2-thiobarbituric acid l-benzoyl-2-thiobarbituric acid 1,5-diacetyl-Z-thiobarbituric acid Examples of alkylolamines suitable for reacting with compounds having the nucleus Example A About 1 mole of l-acetyl-2-thiohydantoin and about two moles of monoethanolamine are dissolved in three liters of ethanol contained Within a suitable reaction vessel. The resultant solution then is heated to boil ofi a portion of the ethanol and reduce the solution to about one liter in volume. The resultant viscous mixture is cooled, filtered, and the filtrate washed with a small amount of ethanol to remove the excess amine. The product is air dried. It has a melting point of 135- l37 C. it is believed that the l-acetyl-Z-thiohydantoin and the monoethanolamine react in the manner indicated by the following equations:

Alcohol Heat This reaction product, when added to acid electrolyte plating baths, brings about an improved smoothness and brightness in copper electrodeposited therefrom.

Example B One mole of acetylthiourea is dissolved in 1.1 moles of triethanolamine contained within a suitable reaction vessel by heating. Upon cooling, a solid reaction product crystallizes from the solution. The product is filtered and washed with a small amount of alcohol to remove the excess amine. The product obtained upon air drying of this washed mass of solid particles is suitable for addition to an acid electrolyte for the purpose of bringing about improved smoothness and brightness of copper electrodeposited therefrom.

Example C 1 mole of acetylthiourea and 1 mole of l-acetyl-Z- thiohydantoin are dissolved in 1.5 moles of monethanolamine and 1 mole of isopropanolamine, and the mixture is heated to a temperature above C. Upon cooling, a solid product crystallizes out of the solution. The crystals are washed with alcohol and are then suitable for addition to a plating bath.

The addition agents of this invention may be employed alone in acid copper plating baths or in combination with certain prior known addition agents. For example, the reaction product of l-acetyl-Z-thiohydantoin and monoethanolamine has been added to a series of acid copper baths containing (1) phenol sulfonic acid, (2) thiourea, (3) glue, and (4) metallic addition agents such as cadmium and the like. In every case, better copper electrodeposits were obtained using the baths containing either the addition agents of this invention alone or in combination with these known addition agents than were obtained using the plating baths which contained only the prior addition agents.

The addition of the novel reaction products prepared as described hereinabove to acid electrolyte plating baths enables the electrodeposition of copper having a highly refined grain size and having smooth, bright surfaces. Many of the disadvantages encountered with addition agents previously known are eliminated by the utilization of the reaction products of this invention in such acid electrolytes.

Improved brightness and smoother copper electrodeposition is obtained when as little as 0.0001 ounce of the addition agent of this invention per gallon of electrolyte is employed in an acid electrolyte plating bath. The addition agent may be employed in amounts up to as high as about 0.05 ounce per gallon. Larger quantities of the addition agents, for example, up to as high as 0.5 ounce per gallon have been used satisfactorily. The optimum proportions are from 0.001 to 0.01 ounce of the reaction product per gallon of electrolyte.

It has been determined that in certain plating baths improved results are obtained by incorporating a minor amount of chlorides, present as the chloride ion, in the plating bath with the addition agents described hereinabove. Commercial hydrochloric acid (37%) may be used for this purpose to provide fro-m about 0.001 ounce per gallon to 0.06 ounce per gallon of chloride ion component depending upon the quantity of addition agent introduced into the plating bath. Alkali metal chlorides such as sodium chloride and other ionizable chloride salts may be added to introduce the chloride ion into the electrolyte.

Acid copper electrolytes suitable .for plating copper are Well known. Ordinarily, .such electrolytes comprise an aqueous solution having dissolved therein from 20 to 40 ounces per gallon of copper sulfate and from 1.3 to 13 ounces per gallon of sulfuric acid. In industry at the present time, one widely usedacid copper bath comprises a solution of 28 ounces per gallon of copper sulfate crystals and 8 ounces per gallon of sulfun'c acid (98%). Into the acid copper electrolyte there may be added the addition agents-of this invention in an amount of from 0.0001 to 0.05 ounce per gallon of electrolyte. The best results have been obtained with from 0.001 to 0.01 ounce of the reaction product per gallon. It will be appreciated that as the electrolyte is used in plating the addition agent will require replenishing from time to time. When treated with these addition agents, very satisfactory copper plating will result when the bath is at any temperature from 40 F. up to about 150 F. Excellent copper deposits have been secured using baths operating at temperatures of from about 70 F. to about 125 F.,-which temperatures appear to define the optimum range.

As a result of numerous tests run under comparable conditions, both in the laboratory and in the shop, it has been determined that these addition agents enable the brightest copper to be deposited that has been secured with any singleknown addition agent, and furthermore the electrodeposited copper is relatively nonbrittle.

Acid copper aqueous electroplating electrolytes with the addition agents of this invention added thereto, with or without organic acids, dextrin, dextrose, or any other additive capable of extending the useful life of the addition agents in the bath or otherwise improving the deposition, as will be set forth hereinafter, may be employed for plating metal by passing either continuous direct current or periodically reversed electrical current or other suitable electrical current therethrough. Excellent results have been obtained with direct current plating from such electrolytes. However, periodic reverse current has given outstanding electro-deposits characterized by an absence of nodules and having edges and surfaces which are substantially smoother than attuinable with direct current.

Referring to the drawing there is illustrated in Fig. 1 an apparatus 10 for practicing the present invention. This apparatus comprises a tank 12 provided with a suitable liner 14 of rubber, glass or the like, resistant to the acid electrolyte, carrying an electrolyte 16 composed of an aqueous solution of copper sulfate, sulfuric acid and an addition agent as described herein. Disposed within the electrolyte is an anode 18 that may be composed of copperor lead, or separate anodes of both. If lead anodes are used, the copper must be replenished by introducing copper sulfate into the electrolyte 16 from time to time. The anode 18 is suspended by-a support 19 from a conductor bar 20. A member 22 to be plated with copper is suspended by a support 24 from a second conductor bar 26. The conductor bars ,20 and 26 are provided with electrical current from a substantially free from brittleness and striations or ribbing. The copper deposited will exhibit a highly refined grain and will be superior to copper deposited from an acid copper electrolyte bath containing many of the other known addition agents.

Copper may be plated from the above described electrolyte containing the addition agent of this invention by means of a periodically reversed electrical current composed of cycles, each of which passes electrical current through the member for a period of time of from 0.01 second to 100 seconds to plate copperon the base andthen the direction of flow of the current is reversed to deplate a part of the previously plated copper. The time and the magnitude of the deplating current is such that it applies from about 8% to 90% of the coulombs applied during the previous plating period. Assuming 100% efiiciency during the deplating period, this means that from 8% to 90% of the copper deposited during the previous plating period in each cycle is deplated. The increment of copper remaining on the base after the cycle consists of smooth, sound copper upon which a, second layer of copper is plated by the plating portion of the next cycle of periodic reversed current and then a portion of this second increment is deplated by passing of deplating current leaving a second'increment of still smoother copper than the first increment, and so on.

Referring to Fig. 2 of the drawing, a graph is shown illustrating one type of periodic reverse current as it is applied to the base. Such periodic cycles may be produced by periodically reversing the flow of uniform direct current. It is assumed that the base when first immersed in the electrolyte is at a zero potential so that no current flows. When the first cycle of periodically reversed current is applied, a cathodic or plating current of a density of the value A is applied and metal is plated for a period of time X to a point B, then the direction of flow of the current is reversed so that the current density in the member drops from the value B to zero and then becomes anodic and will deplate copper, reaching a deplating current density of 'C. Metal is deplated for a period of time Y, which is about atleast of the length of period X, at the current density of C to D until sufficient coulombs of deplating current have been applied to equal from 8% to of the coulombs applied during the plating period X. The cycle A-BCD deposits an increment of sound, smooth copper on the base. The direction of current flow is again reversed from D through zero and then plating current of a density value of F is applied to begin another cycle which will plate a second increment of copper.

It will be understood that the showing in Fig. 2 is merely schematic and that the current density is not necessarily uniform from A to B or C to D, as shown, but will usually vary and be relatively non-uniform. Also in reversing from B to C and from D to F the time required is finite and these lines will not be vertical, as shown, but will take an appreciableperiod of time, depending upon the various factors involved in the plating installation. The deplating or anodic current density C-D may be equal to the plating current density A-B, or exceed it or may be as low as 8% of the plating current density. Reference should be had to Patents 2,451,341,

2,678,909 and 2,470,775 for additional information as to periodic reverse current cycles.

In order to indicate even more fully the advantages and capabilities of the present invention, the following specific examples are set forth to illustrate the utilization of the addition agents of this invention in acid electrolyte plating baths.

Example I An aqueous electroplating electrolyte of the following composition was prepared:

Ozs. per gal. Copper sulfate (crystals) [CuSO .5H O] 28 Sulfuric acid (98%) 8 Reaction product of 1-acetyl-2-thiohydantoin and monoethanolamine (as in Example A) 0.003

Example I using a periodic reverse current having the following cycles:

Plating Deplating time, time, seconds seconds The current density during each portion of the cycles (a) and (b) was 50 amperes per square foot and 60 amperes per square foot for cycles (0) and (d). The current density during the plating portion of cycles (e), (7") and (g) was 75 amperes per square foot. During the deplating period of (e) the current density was 7.5 amperes per square foot (10% reverse coulombs). During the deplating periods of (f) and (g) the current density was 75 amperes per square foot. The periodic reverse current cycles in each case produced excellent smooth deposits of copper better than anything secured under the same conditions using many other addition agents previously known in the art.

In another test, 0.05 ounce per gallon of the reaction product of Z-thiohydantoin and monoethanolamine was used instead of the reaction product employed in Example I. The plating solution produced direct current plated copper deposits on base members fully equivalent to those described in Example I.

In a still further test, 0.0001 ounce per gallon of the reaction product of acetylthiourea and diethanolamine was used instead of the reaction product of Example I. The plating solution produced copper deposits on base members which were semi-bright and of such quality that they required only a very light color buff to prepare them for subsequent bright nickel or chromium deposition.

Example II The following electrolyte was prepared:

Ozs. per gal.

Copper sulfate (crystals) [CuSO .5I-I O1 28 Sulfuric acid (98%) 8 Reaction product of 2-thiohydantoin and monoethanolamine 0.001

.When direct current was applied to the electrolyte, ex-

cellent deposits were produced on base members at cur- 1: rent densities of from 5 to 200 amperes per square foot. A periodic reverse current having a plating portion of 20 seconds and deplating portion of 4 seconds was employed in plating copper on bases from the electrolyte at various current densities of up to 200 amperes per square foot for both portions of the cycle with excellent copper deposits being secured.

Other baths were prepared as in this Example II using progressively larger amounts of the reaction product up to 0.006 ounce per gallon with progressively increasing quality of the deposits. The copper electrodeposited on base members from each electrolyte was characterized by copper of a highly refined grain.

It has been determined that the addition of certain water soluble carboxylic acids or dextrin, or dextrose to acid copper electrolyte baths containing the reaction products of this invention enables these reaction products to function at their maximum efiiciency for longer periods of time than is possible with the reaction products alone. Citric acid, aconitic acid, and oxalic acid are examples of acids which have proven beneficial for this purpose. Any of these or mixtures of two or more may be employed in amounts of from 0.001 ounce up to about 3 ounces per gallon of electrolyte or up to their limit of solubility in the electrolyte. Dextrin or dextrose may be employed in amounts of from about 0.008 to about 0.25 ounce per gallon of electrolyte, though amounts as low as 0.001 ounce and as high as 5.0 ounces per gallon of electrolyte may be used. The dextrin, dextrose and carboxylic acid may be employed singly or in combination of any two or more.

The following examples illustrate the incorporation of some of these latter materials into an acid copper electrolyte bath containing the reaction products of this invention.

Example III Ozs. per gal. Copper sulfate (crystals) [CuSO .5I-I O] 28 Sulfuric acid (98%) 8 Reaction product of l-acetyl-Z-thiohydantoin and monoethanolamine 0.001 Dextrin (yellow) 0.008

The copper deposits plated from this electrolyte had better color than deposits obtained from the electrolyte without the dextrin.

This electrolyte produced bright copper deposits for about twice as many days than was possible using the electrolyte of Example I.

Example IV Ozs. per gal. Copper sulfate (crystals) [CuSO .5H O] 28 Sulfuric acid (98%) 8 Reaction product of l-acetyl-Z-thiohydantoin and monoethanolamine 0.001 Hydrochloric acid (37%) 0.006

The copper deposits obtained using this electrolyte had a slightly better color than those obtained with the electrolyte of Example III, though they were not noticeably brighter in appearance.

Example V 1 Ozs. per gal. Copper sulfate (crystals) [CuSO 5H O] 28 Sulfuric acid (98%) 8 Reaction product of 1-acetyl-2-thiohydantoin and monoethanolamine 0.001

Citric acid 0.25

This electrolyte produced bright copper deposits for a longer period of time than was possible using the electrolyte of Example V.

Another satisfactory plating bath is prepared adding 0.008 ounce per gallon of dextrose to the electrolyte of Example Reaction product of 5-furfural-2-thiohydantoin and methylmonoethanolamine 0.001 Hydrochloric acid (37%) 0.003 Dextrin 0.004

The copper deposits obtained using this electrolyte has a better color and the electrolyte produces such deposits for a longer period of time than the electrolyte of Example I.

While the present invention has been described with particular reference to preferred embodiments thereof, it will be understood, of course, that certain changes, substitutions, modifications and the like may be made therein without departing from its true scope.

I claim as my invention:

1. An aqueous electrolyte plating solution comprising copper sulfate, sulfuric acid and from 0.0001 to 0.5 ounce per gallon of the product obtained by admixing and heating substantially equimolar quantities of at least one compound having the nucleus II I ll with at least one alkylolamine selected from the group consisting of primary, secondary and tertiary alkylolamines in which the groups substituted on the nitrogen atom are selected from the group consisting of hydrogen, alkyl groups, and alkylol groups having from 1 to 4 carbon atoms, there being at least one alkylol group per molecule. 2. An aqueous electrolyte comprising from. 20 to 40 ounces per gallon of copper sulfate, and from 1.3 to 13 ounces per gallon of sulfuric acid and from 0.0001 to 0.5 ounce per gallon of the product obtained by admixing and heating substantially equimolar quantities of at least one compound having the nucleus -C-NC- H I ll with at least one alkylolamine selected from the group consisting of primary, secondary and tertiary alkylolamines in which the groups substituted on the nitrogen atom are selected from the group consisting of hydrogen, alkyl groups, and alkylol groups having from 1 to 4 carbon atoms, there being at least one alkylol group permolecule.

3. An aqueous electrolyte as set forth in claim 2 which contains from 0.001 to 0.06 ounce of chloride ion in each gallon of the electrolyte.

4. An aqueous electrolyte as set forth in claim 2 which contains from 0.001 to 3 ounces of at least one water soluble carboxylic acid in each gallon of the electrolyte.

5. An aqueous electrolyte as set forth in claim 2 which contains from 0.001 to 5 .0 ounces of dextrin in each gallon of the electrolyte.

Hill

with at least one alkylolamine selected from the group consisting of primary, secondary and tertiary alkylolamines in which-the groups substituted on the nitrogen atom are selected from the group'consisting of hydrogen, alkyl groups, and alkylol groups having from 1 to 4 carbon atoms, there being at least one alkylol group per molecule, and then passing a plating electrical current from the anode through the electrolyte and to the member to deposit copper on the member.

8. The process of claim 7 in which there are from 0.00l to 0.06 ounce of chloride ion in each gallon of the electrolyte.

9. The process of claim 7 in which there'are from 0.001 to 3 ounces of at least one water soluble carboxylic acid in each gallon of the electrolyte.

10. The process of claim 7 in which there are from 0.001 to 5.0 ounces of dextrin in each gallon of the electrolyte.

11. The process of claim 7 in which there are from 0.001 to 5 .0 ounces of dextrose in each gallon of the electrolyte.

12. In the process of plating copper on a base member from an acid electrolyte having an anode therein, said electrolyte comprising copper sulfate and sulfuric acid, the improvement which comprises adding from 0.0001 to 0.5 ounce per gallon of the product obtained by admixing and heating substantially equirnolar quantities' of at least one compound having the nucleus -o-N-o- II I ll with at least one alkylolamine selected from the group consisting of primary, secondary and tertiary alkylolamines in which the groups substituted on the nitrogen atom are selected from the group consisting of hydrogen, alkyl groups, and alkylol groups having from 1 to 4 carbon atoms, there being at least one alkylol group per molecule, and then passing cycles of periodically reversed electrical current through the base member, the aqueous electrolyte, and the anode, the electrical current during each cycle first flowing in one direction to plate copper on the member for a period of time of from 0.1 second to 100 seconds, then the direction of current flow reversing for a period of time to deplate a portion of the previously plated copper, the coulombs applied during the deplating period equal to from 8% to of the coulombs applied during the plating period, the plurality of cycles of periodically reversed current electrodepositing smooth sound copper on the base member.

13. .The process of claim 12 in which there are from 0.001 to 0.06 ounce of chloride ion in each gallon of the electrolyte.

14. The process of claim 12 in which there are from 0.001 to 3 ounces of at least one water soluble carboxylic acid in each gallon of the electrolyte.

15. The process of claim 12 in which there are from 0.001 to 5 .0 ounces of dextrin in each gallon of the electrolyte.

16. The process of claim 12 in which there are from 0.001 to 5.0 ounces of dextrose in each gallon of the electrolyte.

References Cited in the file of this patent UNITED STATES PATENTS 2,475,974 Max July 12, 1949 2,538,960 Bernstein Jan. 23, 1951 2,561,689 Doran et al. July 24, 1951 2,700,019 Jernstedt et a1 Jan. 18, 1955 2,742,412 Cransberg et al Apr. 17, 1956 2,799,634 Woehrle et al. July 16, 1957 FOREIGN PATENTS 461,186 Canada Nov. 22, 1949 

1. AN AQUEOUS ELECTROLYTE PLATING SOLUTION COMPRISING COPPER SULFATE, SULFURIC ACID AND FROM 0.0001 TO 0.5 OUNCE PER GALLON OF THE PRODUCT OBTAINED BY ADMIXING AND HEATING SUBSTANTIALLY EQUIMOLAR QUANTITIES OF AT LEAST ONE COMPOUND HAVING THE NUCLEUS 